There is, for example, a touch input device disclosed in Patent Document 1 as a pressing sensor which detects a press on an operation surface. The touch input device described in Patent Document 1 adopts a structure formed by overlaying a pressure-sensitive sensor of a flat shape and a capacitive sensor of a flat shape.
Further, for example, an input device disclosed in Patent Document 2 is also known. The input device disclosed in Patent Document 2 includes an operation surface of a rectangular flat shape. A piezoelectric element is provided in a lower surface of the operation surface. When a user presses the operation surface, the operation surface warps and the piezoelectric element warps, so that it is possible to detect the press.
Patent Document 1: Japanese Patent Application Laid-Open No. 5-61592
Patent Document 2: Japanese Patent Application Laid-Open No. 2012-203552